1. Field of the Invention
The invention relates to a method of reconditioning used wood in which contaminated surface portions are removed by mechanical and chemical operations.
2. The Prior Art
Utilization of used wood as a working material is often particularly problematic because of various contaminations. Most often, the wood is contaminated by organic and inorganic wood preservatives which as a rule are applied to the surface of the wood by drenching or immersion processes, or after construction. Because of the manner in which the wood preservatives have been applied and because of the structure of the wood these wood preservatives are directly fixed only to the surface of the wood, i.e. penetrating not more than few millimeters thereof. Moreover, used wood may be contaminated by inorganic or mineral contaminations from building materials such as, for example, cement, gypsum, concrete or tar paper. These contaminations, because of the nature of utilization of the wood, e.g. to form support or ceiling beams, are also restricted to the surface. In the case of building wood, demolition wood or pallets, nails, screws and staples of iron or ferrous materials are often present. In most cases, they are separated from the chips after cleaning of the wood by magnetic separators and air separators. Together with the types of contamination referred to above, one often encounters weather-induced wear occurring even in protected wood made perceptible by embrittlement and graying of the surface of the wood. In all of the cases described, removal of only a certain surface layer of a piece of wooden building material is necessary, and the remaining core may be used again as good untreated and undamaged wood material. Mechanical reprocessing of used wood by shaving off its surface has been recognized as possible. because of the different and irregular shapes of used wood and its varying sizes, such a process is, however, very complex and expensive. Moreover, machines used for such purposes are subjected to damage from attached minerals or metal parts. For that reason, an economic reconditioning of used wood has hitherto not been possible in cases where surfaces have had to be removed.